Multi-layer headbox

Abstract: The invention concerns a method in the regulation of a multi-layer headbox and a multi-layer headbox for a paper machine/board machine. In the method, for the formation of the different layers in the web, in the multi-layer headbox, at least two pulp suspensions (M₁,M₂) of different pulp concepts are made to flow, said pulp suspensions forming the different layers in the web. The flow of a pulp suspension (M₂) that forms one of the layers in the web is regulated by regulating the component flows (Q 3.1 , Q 3.2 ...Q 3.n ) that constitute said flow and the concentrations of said component flows independently from one another. Hereby, by means of said regulation applied to the particular layer, the total flow of the pulp suspension (M) leaving the headbox is regulated.

Description: The invention concerns a multi-layer headbox of a paper machine or board machine according to the preamble of claim 1, being based on EP-0 462 472. Further relevant prior art is disclosed in DE-A-4 112 347 and GB-2 093 879. In a multi-layer headbox, pulps of different sorts in the vertical direction are fed in the different layers. One or both of the faces of the paper or board formed out of the jet of the headbox are made representative by using, e.g., high-cost and bleached pulp with a high content of fillers. In a three-layer structure, the middle layer is used to constitute the strength and rigidity of the paper/board, whereas the surface layers hide the less expensive and coarser raw-material in the middle of the structure. In a multi-layer headbox, when the grammage is regulated conventionally by profiling the shape of the slice, all the layers are affected at the same time, including the covering surface layers. In such a case, the coverage by the surface material is changed in the regulated area and leaves a striped appearance in the product. The profile-bar construction produces turbulence in the jet and deteriorates the purity of the layers. As is known from the prior art, the direction of the discharge jet of the pulp suspension discharged out of the headbox should differ from the machine direction as little as possible. A directional angle of the discharge jet that differs from the machine direction, which produces distortion of the fibre orientation, has a clear effect on the quality factors of the paper, such as the anisotropy of strength and stretch. The level and variation of anisotropy in the transverse direction also affect the printing properties of paper, such as moisture expansion. In particular, it is an important requirement that the main axes of the directional distribution, i.e. orientation, of the fibre mesh in the paper coincide with the directions of the main axes of the paper and that the orientation is symmetric in relation to these axes. At the edges of the pulp-flow duct in the headbox, of course, owing to the vertical walls, there is a higher friction. This edge effect produces a very strong linear distortion in the profile. Profile faults in the turbulence generator of the headbox usually produce a non-linear distortion in the profile inside the lateral areas of the flow ducts. Attempts are made to compensate for an unevenness of the grammage profile arising from the drying-shrinkage of paper/board by means of a crown formation of the slice, so that the slice is thicker in the middle of the pulp jet. When the paper/board web is dried, it shrinks in the middle area of the web to a lower extent than in the lateral areas, the shrinkage being, as a rule, in the middle about 1...3 % and in the lateral areas about 4...6 %. Said shrinkage profile produces a corresponding change in the transverse grammage profile of the web so that, owing to the shrinkage, the dry grammage profile of a web whose transverse grammage profile was uniform after the press is changed during the drying so that, in both of the lateral areas of the web, the grammage is slightly higher than in the middle area. As is known from the prior art, said grammage profile has been regulated by profiling the thickness of the jet, either by means of a profile bar construction or by regulating the shape of the discharge duct so that the thickness of the jet is regulated larger in the middle area than in the lateral areas. By means of said arrangement, the pulp suspension is forced to move towards the middle area of the web. Said circumstance affects the deviation-angle profile of the direction of the discharge jet, which profile further determines the distortion profile of the fibre orientation. The main axes of the directional distribution, i.e. orientation, of the fibre mesh should coincide with the directions of the main axes of the paper, and the orientation should be symmetric in relation to these axes. In said regulation that profiles the thickness of the jet, a change in the orientation is produced as the pulp suspension flow receives components in the transverse direction. Regulation of the lip of the headbox also produces a change in the transverse flows of the pulp jet even though the objective of the regulation is exclusively to affect the grammage profile, i.e. the thickness profile of the pulp suspension layer that is fed. Thus, the transverse flows have a direct relationship with the distribution of the fibre orientation. In the present application, a headbox is described, by whose means the pulp suspension flow discharged out of a multi-layer headbox can be regulated without a profile bar. With the headbox it is possible to regulate the consistency of the flow locally, and so also the pressure level of said consistency-regulated flow and, thus, the overall flow quantity and the flow velocity while the mixing ratio, yet, remains at its regulated invariable value. By means of the headbox in accordance with the invention, it is possible to control the grammage profile of the paper/board web reliably across the entire web width, and also the fibre orientation profile of the paper/board web across the entire web width in the layer to which the regulation of the grammage is applied. In the headbox in accordance with the invention, the grammage profile is affected by regulating the pulp flow that forms one layer. The multi-layer headbox in accordance with the invention has the features in the characterizing part of claim 1. In the solution in accordance with the invention, two component flows are introduced into the mixer, and the mixing ratio is regulated continuously so that, when the throttle of the pulp flow or 0-water flow in one component-flow duct is increased, the throttle of the other component flow is reduced, or the other way round. Thus, in the regulation, the concentration of the overall pulp flow departing from the mixer is affected continuously and, yet, the quantity of said flow is kept invariable. Thus, to the pulp flow, it is possible to add, for example, water alone, i.e. 0-water, or a diluted pulp suspension whose concentration differs, on the whole, from the concentration of the other component flow. The combined flow constitutes the web layer. In the prior-art solution, the grammage profile was altered by acting upon the thickness profile of the jet discharged out of the headbox. In the equipment in accordance with the invention, a profiling throttle is not needed, because the fibre orientation profile is regulated by means of local flows passed into different positions of width in the headbox. In the solution in accordance with the invention, the multi-layer headbox comprises separate blocks across the width of the multi-layer headbox, in which blocks it is possible to regulate the consistencies of the flows in said blocks to the desired level. For example, when the flow in the middle layer is regulated, by means of the flow it is possible to correct a fault in the grammage profile occurring in a certain width position of the web. Thus, into a certain position of width of the headbox, it is possible to introduce a pulp suspension thicker than average or a pulp suspension more dilute than average, depending on the measured grammage profile error, so as to correct said profile error. However, it is essential in the regulation of the grammage profile that, the flow quantity of the combined flow Q 3 is kept invariable. Thus, during the regulation of the consistency, no changes are produced in the overall flow-velocity profile of the pulp suspension in the headbox. By means of the width-specific flows Q 3.1 ,Q 3.2 ...Q 3.n in the headbox, by means of regulation of the consistency of the flows, the consistency of the pulp suspension is affected at a certain position of width, and thus, by means of each flow Q 3.1 ,Q 3.2 ...Q 3.n , faults occurring in the grammage profile are corrected. Also, with the headbox in accordance with the invention, it is possible to regulate the fibre orientation of the flow discharged out of the headbox by regulating the pressure profile of the flow, and by thereby regulating the velocity profile. This takes place by, in a certain layer, regulating the flow quantity of each flow Q 3.1 ,Q 3.2 ...Q 3.n independently from one another. Thus, when the fibre orientation profile is supposed to be corrected, the flow velocity profile coming out of the pipe system of the turbulence generator is affected locally in the direction of width of the web, and at a certain position of width of the web, locally the pressure level and thereby the flow velocity and further the flow quantity are increased or, if necessary, reduced. In this way it is possible to act upon local profile faults occurring in the fibre orientation of the web. Next, the invention will be described with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1 is a sectional view of a multi-layer headbox of a paper machine in accordance with the present patent application. Figure 2A is a sectional view taken along the line I-I in Fig. 1. Figure 2B is a sectional view taken along the line II-II in Fig. 1. Figure 2C is a sectional view taken along the line III-III in Fig. 1. Figure 2D is a sectional view taken along the line IV-IV in Fig. 1. Figure 3 is a partial illustration of principle of a mixer unit, by whose means a fault in the grammage profile and a fault in the fibre orientation profile can be corrected locally in the direction of width of the web. Figure 4A is an illustration of principle of a first position of regulation. Figure 4B shows a second position of regulation. Figure 4C shows a third position of regulation. Figure 5A shows an embodiment of a mixer unit in accordance with the invention which corresponds to the illustrations of principle in Fig. 3 and in Figs. 4A...4C. Fig. 5A is a sectional view of the mixer unit in accordance with the invention. Figure 5B is an illustration in the direction K 1 indicated in Fig. 5A. Figure 5C is an illustration in the direction K 2 indicated in Fig. 5A. Figure 5D is an illustration in the direction K 3 indicated in Fig. 5A. Figure 5E is an axonometric view of the distributor part of the mixer unit shown in the preceding figures 5A...5D. Figure 6A is a sectional view of an embodiment of a mixer unit, wherein the flow into the inlet chamber of the mixer unit is distributed by means of a separate tumbler piece, which is placed in different closing positions in relation to the inlet openings, in which case, when one inlet opening is being opened, the other inlet opening is closed by the corresponding amount. Figure 6B is a sectional view taken along the line V-V in Fig. 6A. Figure 7A shows an embodiment of the invention in the other respects corresponding to Figs. 6A,6B, except that in this embodiment the pressure level of the departing flow Q can also be regulated. Figure 7B is a sectional view taken along the line VI-VI in Fig. 7A. Fig. 1 shows a multi-layer headbox as per the invention in connection with a twin-wire former. Of the former, Fig. 1 shows the breast rolls 10 and 11 and the forming wires 12 and 13 running over them, said forming wires defining the forming gap G between them. The discharge duct 14 of the headbox comprises flaps 16a 1 ,16a 2 ..., and out of the discharge duct 14 of the headbox, the pulp suspension jet is fed through the slice 15 into the forming gap G defined by the wires 12 and 13. Proceeding in the flow direction F of the pulp suspension, the headbox comprises inlet headers 100,110,120,130, distributor manifolds, a turbulence generator 19, and a discharge duct 14. The discharge duct 14 is defined by a stationary lower-lip wall 20 and by an upper-lip wall 21 pivoting around a horizontal articulated joint G. In the multi-layer headbox, a first pulp suspension M 1 is passed out of the inlet header 100 through the distributor manifold 101 into the intermediate chamber J 1 and further to the throttle 102 and further to the turbulence generator 19 into its turbulence tubes 19a 1 . Similarly, a second pulp suspension M 3 , whose composition may be the same as that of the first pulp suspension M 1 or different from same, is brought from the inlet header 110 through the distributor manifold 111 into the intermediate chamber J 2 and through the throttle 112 to the turbulence generator 19 into its turbulence tubes. The flow Q 3.1 ,Q 3.2 ...Q 3.n of the third pulp suspension M 2 is composed of component flows Q 1.1 ,Q 1.2 ...Q 1.n and Q 2.1 ,Q 2.2 ...Q 2.n . Each component flow Q 1.1 ,Q 1.2 ...Q 1.n is brought from the inlet manifold 120 and passed through the distributor pipes 23a 1 ,23a 2 ... into its own mixer unit 22a 1 ,22a 2 ...22a n in the direction of width. From the other inlet header 130, the second component flow Q 2.1 ,Q 2.2 ...Q 2.n is passed through the distributor pipe 24a 1 ,24a 2 into the mixer unit 22a 1 ,22a 2 ...22 an . In the mixer units 22a 1 ,22a 2 ...22a n the component flows Q 1.1 ,Q 1.2 ...Q 1.n and Q 2.1 ,Q 2.2 ...Q 2.n are mixed together, and the combined flow Q 3 , which forms a pulp suspension (Q 1.1 + Q 1.2 ; Q 2.1 + Q 2.2 ) M 2 , is passed, in the way illustrated in the figure, as the middle flow into the intermediate chambers 28a 1 ,28a 2 ..., which have been divided into compartments in the direction of width, or into pipes, and further into the turbulence generator 19 into the tubes 19a 2 of the turbulence generator placed in a corresponding relative height position. The discharge duct 14 comprises flaps 16a 1 ,16a 2 ...16a n . When the pulp suspensions M 1 ,M 2 and M 3 are passed in the way described above, having been divided into blocks in the vertical direction, mixing together of said pulp suspensions is prevented and, by means of said pulp suspensions M 1 ,M 2 and M 3 , the web layers T 1 ,T 2 and T 3 are formed. Further, in the solution in accordance with the present invention, the flows Q 3.1 ,Q 3.2 ...Q 3.n of the middle pulp suspension M 2 are regulated in the direction of width of the paper machine by means of the mixer units 22a 1 ,22a 2 ...22a n and, thus, on the whole, the flow of the overall pulp suspension M departing from the multi-layer headbox is regulated by means of said regulation of the middle layer. The concept and the composition of the pulp M 2 differ from the composition and the concept of the pulp M 1 of the surface layer and preferably also from the composition and the concept of the pulp M 3 . Within the scope of the invention, it is, of course, possible that the multi-layer headbox comprises means for the formation of two web layers only or means for the formation of more than three web layers. Within the scope of the invention, an embodiment of the invention is, of course, also possible in which intermediate chambers are not needed for the pulp flows M 1 and M 3 . In such a case, the pulps M 1 and M 3 are made to flow out of their inlet headers directly through pipes into the turbulence generator 19. Fig. 2A is a sectional view taken along the line I-I in Fig. 1. As is shown in the figure, the pulp M 1 is passed out of the inlet header 100 into the distributor pipes 101a 1 ,101a 2 ...101a n and further into the intermediate chamber J 1 and through the throttles 102a 1 ,102a 2 ...102a n further into the turbulence generator 19 into its turbulence tubes 19a 1 , from which the pulp M 1 flows into the discharge duct 14 and is not mixed with the other pulp layers M 2 ,M 3 . Fig. 2B is a sectional view taken along the line II-II in Fig. 1. The sectional view of Fig. 2B corresponds to the sectional view in Fig. 2A, because the arrangement of introduction of the pulp M 3 is similar to that of the pulp M 1 . The pulp M 3 is passed from the inlet header 110 into the distributor pipes 111a 1 ,111a 2 ... and further into the intermediate chamber J 2 and through the throttles 112a 1 ,112a 2 ... further into the turbulence generator 19 into its turbulence tubes 19a 3 and further into the discharge duct 14. Fig. 2C is a sectional view taken along the line III-III in Fig. 1. As is shown in Fig. 2C, the component flow Q 1 , which is preferably a diluting water flow, is passed from the inlet header 120 through the ducts 23a 1 ,23a 2 ...23a n and further into the mixer unit 22a 1 ,22a 2 ...22a n and further from the mixer unit, having been mixed with the flow Q 2 , into the duct 25a 1 of the mixer unit and into the distributor pipe/compartment 28a 1 ,28a 2 ... and further through the throttle D 1 ,D 2 ... into the turbulence generator 19 into its turbulence tube 19a 2 and, in a corresponding vertical height position, into the space between the flaps 16a 1 ,16a 2 in the discharge duct 14. Fig. 2D is a sectional view taken along the line IV-IV in Fig. 1. As is shown in the figure, the flow Q 2 is passed to the mixer unit 22a 1 ,22a 2 ...22a n from the inlet header 130, and it is essential that the concentration of the flow Q 2 differs from the concentration of the flow Q 1 . Preferably, the flow Q 1 consists of diluting water, and the flow Q 2 consists of pulp. From the inlet header 130 the flow Q 2 is passed into the pipes 24a 1 ,24a 2 ... and into each particular mixer unit 22a 1 ,22a 2 ..., in which the flows Q 1 and Q 2 are mixed at a certain mixing ratio, and the combined flow Q 3 is passed through the duct 25a 1 ,25a 2 ... into the compartment 28a 1 ,28a 2 of the distributor pipe and further through the throttles D 1 ,D 2 ... into the turbulence generator 19 into each particular turbulence tube 19a 2 and into the discharge duct 14, as was already described in relation to the preceding figure. Fig. 3 is an illustration of principle of a mixer unit 22 in accordance with the invention, by whose means it is possible to supply a pulp flow of desired consistency to a certain pulp suspension layer and to a certain position of width of the multilayer headbox. By means of the mixer unit shown in Fig. 3, it is possible to regulate the grammage profile. In a corresponding way, by means of the mixer unit, it is possible to regulate the fibre orientation profile by acting upon the pressure loss in the pulp flow passing through the mixer unit and, thus, upon the velocity of the flow and further upon the flow quantity. Fig. 3 is an illustration of principle. The mixer unit 22 comprises a first inlet duct 23, through which the component flow Q 1 , preferably a so-called 0-water flow, is introduced into the chamber F of the mixer unit. Further, the mixer unit 22 comprises a second duct 24, through which the second component flow Q 2 , which is preferably a component flow at the average concentration of the pulp suspension, is introduced into the chamber F of the mixer unit 22. The flows pass, at the consistency ratio distributed by the distributor part 26, through the transverse duct 27 of the distributor part 26, placed in the chamber F, into the outlet duct 25. The combined flow Q 3 = Q 1 + Q 2 is passed to a certain position along the width of the headbox of the paper machine. According to the invention, each position of width of the paper machine comprises a separate duct 28a 1 ,28a 2 ..., in front of which there is a mixer unit 22a 1 ,22a 2 ,22a 3 ..., by whose means it is possible to regulate the concentration of the pulp suspension departing from the mixer units, and favourably also the flow velocity of said pulp suspension and, thus, the flow quantity. In the way shown in Fig. 3, the distributor part 26 can be displaced along a linear path (arrow L 1 ) in the chamber F, and said distributor part 26 can also be rotated (arrow L 2 ) in the chamber F. In such a case, the mouth part 27a of the flow duct 27 extending across the distributor part 26 can be brought into different positions in relation to the end openings 23a,24a of the inlet ducts 23 and 24. Thus, the flows Q 1 ,Q 2 in the ducts 23 and 24 can be regulated by increasing the throttle, i.e. the flow resistance, of the flow Q 1 in the duct 23 and reducing the throttle, i.e. the flow resistance, of the flow Q 2 in the duct 24, or the other way round. By shifting the distributor part 26 along a linear path, the mixing ratio of the flow Q 3 is affected, and when the distributor part 26 is rotated, the pressure loss in the combined flow Q 3 is affected. Fig. 4A is an illustration of principle of a regulation in accordance with the invention. In the regulation position of Fig. 4A, the flow has access through the sectional flow areas U 1 and U 2 denoted by the shading into the duct 27 in the distributor part 26. The end opening of the duct 23 is denoted with 23a, and the end opening of the duct 24 is denoted with 24a. The sectional flow area of the end opening 23a is A 1 , and it corresponds to the sectional flow area of the end opening 24a. The shapes of the openings 23a and 24a are similar to one another. The central axis of the opening 23a is denoted with X 1 , and the central axis of the opening 24a is denoted with X 2 . The connecting line of the axes X 1 and X 2 is denoted with Y in the figure. The orifice of the flow duct 27 in the regulation part 26 is denoted with 27a in the figure. When the overall flow quantity Q 3 is increased, at the same time, the sectional flow area U 1 ,U 2 is increased through which the flow takes place into the duct 27 in the regulation part 26 and (in the way shown in the figure) the distributor part 26 is raised or lowered perpendicularly to the line Y (in the direction N). In a corresponding way, when exclusively the mixing ratio of the flows Q 1 ,Q 2 is supposed to be changed, the orifice 27a is displaced in the direction N', which is perpendicular to the direction N. The flow openings 23a,24a are arranged in such a way in relation to one another that at least one of the central planes coincide and that at least one central planes perpendicular to said central planes are parallel to one another. In Figs. 4A...4C, a solution as shown in the embodiment of Fig. 3 is examined, wherein the distributor part includes a duct 27, but it is obvious that the above examination also applies to the solution of the embodiment shown in Fig. 6, in which the distributor part 260 is a tumbler part, which does not include a separate transverse duct and by means of which tumbler part the end openings 23a,24a of the ducts 23,24 for the component flows are closed and opened. When the distributor part 26 is shifted along a linear path in the way shown in Fig. 4B, the sectional flow area U 1 of the component flow Q 1 coming from the duct 23 is increased, and the sectional flow area U 2 of the component flow Q 2 is reduced in the corresponding proportion. Thus, in the regulation, the mixing ratio is changed, but the sum of the flow quantities Q 3 = Q 1 + Q 2 remains invariable. If it is desirable to act upon the sum Q 3 of the flows in the way shown in Fig. 4C, the distributor part 26 is shifted to the side (arrow L 2 ), in which case, at the same time, the sectional flow areas U 1 and U 2 are reduced. When the sectional flow areas U 1 ,U 2 are increased, the mixing ratio must remain unchanged. If U 1 was, in the initial situation, larger than U 2 , U 1 is increased by a larger amount than U 2 . In a corresponding way, when the sectional flow areas U 1 and U 2 are reduced, and if U 1 is larger than U 2 , the reduction of U 1 must be greater than the reduction of U 2 . The valve solution in accordance with the invention achieves the keeping of the mixing ratio invariable in the regulation of the flow quantity. Thus, in said regulation of the flow quantity, when the distributor part 26 is rotated, the pressure loss of the flow is affected, and thereby the velocity profile of the flow and further the fibre orientation profile are affected. The regulation does not affect the concentration of the flow Q 3 , and thereby the concentration D 3 of the pulp suspension in the overall flow Q 3 flowing out of the duct 25 is kept at its desired regulated value. Fig. 5A is a sectional view of a first preferred embodiment of a mixer unit in accordance with the invention, which corresponds to the illustrations in Figs. 3 and 4A...4C. As was described above, the mixer unit 22 comprises a first inlet duct 23 and a second inlet duct 24 as well as an exhaust duct 25. The mixer unit comprises a chamber F, in which the distributor part 26 is fitted to be displaceable along a linear path (arrow L 1 ) and in which it is fitted to be rotatable (arrow L 2 ). When the distributor part 26 is displaced along a linear path perpendicularly to the inlet axes X 1 ,X 2 and X 3 of the ducts 23,24,25 (arrow L 1 ), the position of the inlet opening 27a of the transverse duct 27 in the distributor part 26 in relation to the end opening 23a of the first inlet duct 23 and to the end opening 24a of the second inlet duct 24 is affected. Thus, when the distributor part 26 is raised or lowered (arrow L 1 ), the flow is increased through the first inlet duct 23 into the transverse duct 27 in the distributor part 26, and the flow through the second inlet duct 24 is reduced by the corresponding amount, or the other way round. Thus, the mixing ratio between the component flow Q 1 coming from the inlet duct 23 and the component flow Q 2 coming from the other inlet duct 24 is changed, but the overall flow quantity Q 3 = Q 1 + Q 2 of said component flows Q 1 ,Q 2 is kept invariable. Out of the first inlet duct 23, preferably 0-water is made to flow. Out of said flow duct 23, it is also possible to pass a pulp suspension whose concentration is, on the whole, different from the average concentration of the pulp suspension in the headbox, the pulp of average concentration being made to flow preferably through the second inlet duct 24. When the distributor part 26 is rotated (arrow L 2 ), at the same time the throttle of the flow Q 1 coming out of the first inlet duct 23 and the throttle of the flow Q 2 coming out of the second inlet duct 24 are affected so that the flow resistances of said flows out of the ducts 23 and 24 are increased or reduced at the same time. Thus, by rotating the distributor part 26, the pressure loss of the combined flow Q 3 = Q 1 + Q 2 is affected. When the pressure loss is increased or reduced, the flow quantity of the flow Q 3 through the outlet duct 25 is increased or reduced. In this way it is possible to affect the velocity profile of the flow and further the pulp fibre orientation profile at the desired position along the width of the paper machine in the desired way. Fig. 5B is an illustration in the direction K 1 indicated in Fig. 5A. Fig. 5C is an illustration in the direction K 2 indicated in Fig. 5A. Fig. 5D is an illustration in the direction K 3 in Fig. 5A, i.e. from above. Fig. 5E is an axonometric illustration of a disassembled distributor part 26 of the mixer unit 22 in accordance with the invention. Fig.6 is a sectional view of an embodiment of a mixer unit 22 falling outside the scope of the claims. Also in this embodiment, the mixer unit 22 comprises a first inlet duct 23 and a second inlet duct 24 and an outlet duct 25, through which the combined flow Q 3 = Q 1 + Q 2 is removed. The distributor part 260 comprises a displacing spindle 260a, by whose means the distributor part 260 can be shifted into different covering positions in relation to the end opening 23a of the first inlet duct 23 and in relation to the end opening 24a of the second inlet duct 24. Through the first inlet duct 23, preferably 0-water is introduced. It is also possible to make such a pulp suspension flow through the duct 23 whose concentration is, on the whole, different from the average concentration of the pulp suspension in the headbox, said pulp suspension of average concentration being made to flow preferably through the second inlet duct 24. Thus, in the way shown in Fig. 6A, when the spindle 260a is rotated (arrow L 3 ), the distributor part 260, which operates as a tumbler part, is shifted into different covering positions in relation to the end openings 23a,24a. When the distributor part 260 is displaced, the end opening 23a of the inlet duct 23 is opened, and the end opening 24b of the inlet duct 24 is closed by the corresponding amount, or the other way round. Thus, also in this embodiment of equipment, the mixing ratio can be regulated continuously and, yet, the flow quantity of the combined flow Q 3 remains invariable, i.e. the pressure loss remains at its invariable value. The duct 25 is passed to the desired position of width of the headbox of the paper machine. Thus, in the direction of width, the headbox of the paper machine comprises a number of ducts 25a 1 ,25a 2 ..., which are opened preferably into separate distribution pipes 28a 1 ,28a 2 , each of which passes directly into a turbulence tube 19a 1 ,19a 2 ... of its own placed in the same position of width in the turbulence generator 19. Fig. 6B is a sectional view taken along the line V-V in Fig. 6A. The spindle 260a is rotated by means of the lever 260b. Fig. 7A shows an embodiment of the invention which is in the other respects similar to the embodiment of Figs. 6A and 6B, but in the solution of said embodiment, the flow quantity of the departing flow can also be regulated so that the mixing ratio remains at its regulated invariable value. In the solution of Fig. 7A, the spindle 260a is displaced along a linear path in the way indicated by the arrow L 5 , in which case the distributor part 260 connected with the spindle is placed in different covering positions in relation to the end openings 23a,24a so that, at the same time, the end openings 23a,24a are closed or opened. The regulation of the mixing ratio takes place so that the spindle 260 is rotated in the way shown by the arrow L 4 , whereby the distributor part 260 is shifted into different covering positions in relation to the end openings 23a,24a, and so that, when the sectional flow area of one end opening is increased, the sectional flow area of the other opening is reduced by the corresponding amount, and the other way round. Fig. 7B is a sectional view taken along the line VI-VI in Fig. 7A. In the way indicated in Fig. 7B by means of the arrow L 5 , the distributor part 260 can be shifted along a linear path, whereby, at the same time, the end openings of the ducts 23 and 24 are opened or closed, in which case the throttle of the outlet flow Q 3 is reduced or increased while the mixing ratio of the flows Q 1 and Q 2 remains at its invariable value.

Claims: Multi-layer headbox for forming a multi-layer paper or board web comprising a turbulence generator (19) and a discharge duct (14), in which headbox a first pulp suspension flow (M 2 ) for forming one of the layers of the web is passed in the turbulence generator (19) and further into the discharge duct (14), whereby said first pulp suspension flow (M 2 ) is composed of several adjacent flows (Q 3.1 , Q 3.2 , ..., Q 3.n ) which are passed into the turbulence generator (19) at different points across the width thereof, each of said adjacent flows (Q 3.1 , Q 3.2 ,..., Q 3.n ) being formed by the outlet flow from a mixer unit (22a 1 , 22a 2 , ..., 22a n ) into which two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1, Q 2.2 , ..., Q 2.n ) of different concentrations, i.e. provided from two different sources (120, 130), are introduced by means of two inlets ducts (23a 1 , 23a 2 , ..., 23a n ; 24a 1 , 24a 2 , ..., 24a n ), the two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2.n ) being combined in the mixer unit (22a 1 , 22a 2 , ..., 22a n ), wherein the concentration of each of the adjacent flows (Q 3.1 , Q 3.2 , ..., Q 3.n ) can be regulated by adjusting the mixing ratio of the two component flows (Q 1.1 , Q 1.2, ..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2.n ) from which each of the adjacent flows (Q 3.1 , Q 3.2 , ..., Q 3.n ) is formed while the flow rate of the combined flow (Q 3.1 , Q 3.2 , ..., Q 3.n ) remains constant, and wherein the flow rate of each of the adjacent flows (Q 3.1 , Q 3.2 , ..., Q 3.n ) can be regulated without affecting the concentration thereof, characterized in that the headbox further comprises an inlet header (100) from which a second pulp suspension flow (M 1 ) for forming another layer of the web is passed through distributor pipes (101a 1 , 101a 2 , ..., 101a n ) into the turbulence generator (19) and further into the discharge duct (14), and that each of the mixer units (22a 1 , 22a 2 , ..., 22a n ) comprises: a chamber (F), into which the two component flows (Q 1.1 , Q 1.2 ,..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2.n ) are introduced by means of said two inlet ducts (23a 1 , 23a 2 , ..., 23a n ; 24a 1 , 24a 2 , 24a n ), and a distributor part (26, 260) in the chamber (F), which distributor part (26, 260) can be displaced both along a linear path and rotatively in order to be brought into different covering positions in relation to the end openings (23a, 24a) of the inlet ducts (23a 1 , 23a 2 , ..., 23a n ; 24a 1 , 24a 2 , ..., 24a n ) into the chamber (F) to close or open said end openings (23a, 24a), so that, by one of said displacements, the throttle of one of the two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2n ) is increased and the throttle of the other one of the two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2.n ) is reduced by the corresponding amount, whereby the concentration of the outlet flow (Q 3.1 , Q 3.2 , ..., Q 3.n ) from the mixer unit (22a 1 , 22a 2 , ..., 22a n ) is regulated while the flow rate of said outlet flow (Q 3.1 , Q 3.2 , ..., Q 3.n ) remains constant, and so that, by the other one of said displacements, the throttles of the two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1 , Q 2.2 , ...Q 2.n ) are increased or reduced simultaneously while the mixing ratio of the two component flows (Q 1.1 , Q 1.2 , ..., Q 1.n ; Q 2.1, Q 2.2 , ...Q 2.n ) remains constant, whereby the flow rate of the outlet flow (Q 3.1 , Q 3.2 , ..., Q 3.n ) from the mixer unit (22a 1 , 22a 2 , ..., 22a n ) can be regulated without affecting the concentration thereof, whereby, by regulating the first pulp suspension flow (M 2 ), the total flow of pulp suspension (M) leaving the headbox can be regulated. Multi-layer headbox as claimed in claim 1, characterized in that said distributor part (26) comprises a duct (27) having an opening (27a) which can be brought into different positions in relation to said end openings (23a, 24a). Multi-layer headbox as claimed in claim 1, characterized in that said distributor part (260) is a displaceable tumbler part, which can be brought into different covering positions in relation to said end openings (23a, 24a). Multi-layer headbox as claimed in claims 1 to 3, characterized in that said distributor part (26, 260) is connected to a spindle (26a, 260a), by means of which the distributor part (26, 260) can be displaced.

Inventors: HUOVILA JYRKI, NYBERG PETRI, ODELL MICHAEL, HUOVILA, JYRKI, NYBERG, PETRI, ODELL, MICHAEL
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F1
IPC codes: D21F1